Rotary pump and motor hydraulic transmission



March 6, 1956 BERRY 2,737,020

ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION Filed Oct. 25, 1949 5Sheets-Sheet 1 M is IN V EN TOR.

FRANK BERRY BY fittorney F. BERRY March 6, 1956 ROTARY PUMP AND MOTORHYDRAULIC TRANSMISSION Filed Oct. 25, 1949 5 Sheets-Sheet 2 l INVENTOR.FRANK 35m) z W flttormey F. BERRY March 6, 1956 ROTARY PUMP AND MOTORHYDRAULIC TRANSMISSION INVENTOR. FRANK B'fi/FY BY Lfiorney F. BERRYMarch 6, 1956 ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION 5Sheets-Sheet 4 Filed Oct. 25, 1949 v! RE B mK V N J F. BERRY March 6,1956 ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION Filed Oct. 25, 1949 5Sheets-Sheet 5 Unitd5t tes Pat r-i ROTARY PUMP AND MOTOR HYDRAULIGTRANSMISSION Frank Berry, Corinth, Miss., assignor, by mesneassignments, to Oliver Iron and Steel Corporation, Pittsburgh, Pa ecorporation of Pennsylvania Application October 25, 1949, Serial No.123,504

4 Claims. (Cl. 60-53) h n nti n relates to aut ma a ly iabl by.

r lio po r n mi nd. s pp c ble to ansmissions for motor cars and trucks,tractors, railroad oino os c ft i ar n ora t,v r s f ta i nary machines,or in other words to virtually any type of installation where a variablepower transmission may e emp oy d.

Summary My invention comprises in its general arrangement a ot yhydraulic pump n a rotary hy a ic motor. hydraulically coupled throughconnected'fluid inlets. and; outlets and mechanically coupled throughconnected rot ry. el m nt a yr t ta le h it wh h. ons itutes. both thefluid-driven shaft ofthe motor and a, rotary eler. In. my pr fe d onstruti n. the.

meat o h p mp.- oonnao e ro a y e emen f h m or nd. Pump are con t tted. by a shaft m o to he n r ndnutnp. which units are of what iscommonly known as the rotaryabutment typ T sha pr ferab y. is rran e toserve asthe rotaryabutment valve of both themotonangh Pump units.

n. mpor n fe ur f my i n on as. mbo i in; the. preferred construction tobe described is the'pro vision for relativebodily rotation between the.pumpv an mo s. y ar n h Pu pi y otation- With. this arrangement: the

Hound the abutment shaft. rate of fluid discharge from the pump isautomatically varied in accordance with changes in the relative speedsof; the driven shaft of the motor andthe bodily rotating pump, orinaccordance with the diflferential between-the relative-speeds of bodilyrotation ofthepump and motor nd esp d-o t o fthaomm n shatter con--nected rotary elements ofthe two units.

The motor itself also embodies a variable torque arr rangement suchasprovided'byrotary fluid-drive'n'members connected in parallel to thefluid outlet: andinlet of the .pump, with a valve operable in responseto changes in pressure in the fluid discharged from thepumpto open theconnection to one or more of -suchrotary fluid driven, members andthereby vary the torque ratio be tweenthe pump and motor. Further, in mypreferred, construction this .valve is arranged to close the connection;to all of such rotary fluid-driven members under low; torque. ratioconditions tothereby close the outlet of the response to changes influid pressure within the pumpforby-passing fluid directly from the pumpoutlet to the; pump inlet under low pressure idling conditions, and for:closing theby-pass to transfer fluid to the motonunder highpressuredriving conditions. In my preferred construction this bypass valvecomprises two connected pistons-s of diiferent sizes to create apressure: differential.

"ice

the bypass beingarranged to be closed by the smaller of the two pistons.A fluid connection on the high pressure side of the valve is arranged tohold the valve in closed position under high pressure or drivingconditions. Another fluid connection from the low pressure side of thevalve to a central portion of the differential piston maintains thepressure differential for holding the valve in closed position underconditions where pressure is re versed in the pump, as in decelerationof the pump or of' the hydraulic motor operated thereby, or of both thepump and the motor.

Automatic hydraulic transmissions as developed heretofore primarily fordriving motor cars, tanks, etc. have proved very successful and aretoday gaining wider and: wider acceptance notwithstanding certainrecognized disadvantages as compared with conventional non-auto-. matictransmissions employing a manual gear shift and clutch. One suchdisadvantage is a certain loss in efficiency peculiar to thosecommercial automatic trans missions in which the driving fluid isconstantly in motion at high velocities, and in which an appreciableamount of slippage occurs between the mechanical parts of the. drive dueto the fact that there is no positive hydraulic or mechanical blockbetween them. This problem has. been considered to be of suflicientlyserious consequence. that at leastone large motor manufacturer hasdeveloped an automatic transmission which includes a separate.mechanical clutch to make it possible to obtain a frictional' lock intop speed or overdrive.

Another disadvantage of automatic hydraulic trans? missions now used inautomotive drives is that their construction is complicated andexpensive, so expensive in fact that motor car manufacturers have beencompelied'to reject the automatic transmission for Standarcl' modelcarsand to include it only as an optional extra ata substantially increasedprice to the buyer.

It is the primary object of my invention to overcome these and otherdisadvantages of automatic hydraulic transmissions heretofore known orused, i. e. to make it possible to achieve higher efficiencies and lowerconstruction costs.

Description Ashas been noted at the outset, the invention is applicableto automatic transmissions for use wherever an automatic variable torquedrive is required. Perhaps the largestfield of use is in drives forautomotive vehicles, so throughout the following description I shallrefer moreparticularly to automotive drives as used forexampleinautomobiles. However it will be understood that the features ofthe preferred embodiment illustrated in the drawings are applicable totransmissions for, other purposes. The embodiment selected forillustration isrep resentative of the construction which I presentlycon-.- sider best.

Fig. 1 is a side elevational view of the transmission. This view isdrawn to a reduced scale and is intended-1 primarily as an index to thevarious cross-sectional views.

Fig. 2 is a central horizontal longitudinal sectional view of:thecomplete transmission taken as indicated at: 2.2-in-Fig. 1.

Fig... 3 is a vertical transverse sectional View taken. through theannular cylinders of the pump as indicated at 3.-.3. in Figs. 1 and 2.

Fig.- 4 is an enlarged detail horizontal sectional viewtaken asindicated at 4- 3 in Figs. 1 and 5 and showing theconstruction of theautomatic valvescontrolling the torque ratio within the motor unit, andthe manual selector for forward, neutral and reverse operation. Thisview. shows the selector in forward position with the: valves inthepositions which they occupy in what may be described as the third speedforward.

Fig. 5 is a vertical transverse sectional view taken;

a) through the annular cylinders of one of the sections of the motor.This view is on line -5 of Fig. 4 to reduced scale.

Figs. 6, 7 and 8 are detail cross-sectional views of the pump by-passmeans taken as indicated at 66, 77 and 88 respectively in Fig. 3.

Fig. 9 is a fragmentary end view of the valve housing with parts shownin section on line 9-9 of Fig. 4.

Fig. 10 is a view similar to Fig. 4 but drawn to a smaller scale andshowing the valves in neutral position.

Fig. 11 is an end view of the motor with the end cover plate partlybroken away to reveal the porting.

Figs. 12 and 13 are detail cross-sectional views taken as indicated at12-12 and 13-13 respectively in Fig. 10.

Fig. 14 is a diagrammatic representation of the complete transmission.

Referring particularly to Fig. 2, the transmission selected toillustrate my preferred construction comprises a rotary hydraulic pumpindicated generally at 15 and a rotary hydraulic motor indicatedgenerally at 16 with interconnected fluid inlets and outlets arranged todrive the motor hydraulically from the pump. The driven shaft 17 of themotor extends beyond the end of the motor housing (to the right asviewed in Fig. 2) for connection integrally or otherwise to a rotaryelement 18 of the pump. In the construction shown this rotary element 18is an integral part of shaft 17, which I consider to be the mostadvantageous arrangement. However it will be understood that motor shaft17 and rotary pump element 18 could be formed as separate elements solong as they are coupled together for rotation at the same speed or at afixed speed ratio, so that the action of the pump is modified inaccordance with the speed of shaft 17 in the manner which will bedescribed.

The connected fluid inlets and outlets of the pump and motor comprisefluid passages 19 and 20, the high pressure fluid discharged from thepump entering the motor via passage 19, and the low pressure fluidreturning from the motor via passage 20. Pump 15 is suitably connectedto a prime mover as by means of a coupling flange 21 fixed to driveshaft 22 of an internal combustion engine. Coupling flange 21 may besecured by screws 23 to the cover plate 24 of the pump housing. The pumpis bodily rotated by shaft 22 relative to motor 16 about the axis ofshaft 17, 18 and preferably constitutes the flywheel of thetransmission. If desired, gear teeth 86 may be provided around theperiphery of cover plate 24 for engagement by the gear of a suitableelectric starter for cranking the prime mover.

Referring to Figs. 2 and 3, the rotary abutment type pump shown is builtup of a series of plate-like housing members 25, 26 and 27, and endcover plates 24 and 28. These members are secured together by a seriesof bolts 29 passing through alignment sleeves 30 or extending throughaligned apertures in the various housing members and screwing into coverplate 24. Housing members 25, 26 and 27 have aligned openings to receivethe end 18 of shaft 17 and to receive the piston rotor shafts 31, 31whose axes are spaced from and parallel to rotary abut ment 18. Suitablebearings for the rotor shafts 31 are provided in housing members 25 and27, as clearly shown in Fig. 2. Housing member 25 is recessed at 32 toform a chamber for pinions 33 fixed to piston rotor shafts 31 forengagement with gear teeth 34 on the abutment rotor 18. In theembodiment shown, the driving ratio between pinions 33 and gear 34 is1:1. As shown best in Fig. 3, housing member 26 is formed withcylindrical recesses 35 intersecting the opening for rotary abutment 18.Piston rotors 36 fixed to shafts 31 have pistons 37 slidably engagingthe surfaces of recesses 35 and rotatable in the annular cylinders 33formed between housing mem- The automatic pump by-pass meansincorporated in the pump unit 15 will now be described with reference toFigs. 3 and 5 to 8 inclusive. It, comprises a bypass channel 41connecting the high pressure outlet 42 of the pump with the low pressurefluid inlet 43. A valve channelway 44 (Fig. 6) arranged transversely ofby-pass 41 extends through housing member 26 and into member 25.Coaxially arranged with valve channelway 44 is a channel 45 slightlylarger in cross-sectional area than channelway 44. A differential pistonvalve 46 is slidably arranged in these channelways. This valve comprisestwo connected pistons of different sizes, a smaller piston 47 and alarger one 48. By-pass 41 is arranged to be closed by the smaller of thetwo pistons, but under low pressure idling conditions is held in theopen position shown in Fig. 6 by means of a compression spring 49, thedegree of compression being adjustable by means of the screw-threadedmounting at its end. A fluid connection, such as provided by the smallbore 50, extends from the high pressure fluid outlet 42 to the end ofvalve channelway 47, i. e. to the chamber at the end of the smallerpiston 47. Another fluid connection, such as provided by the small bore51, extends from the low pressure inlet 43 to the central reducedportion of the differential piston 46. The purpose of spring 49 is tohold the valve in open position under low pressure idling conditions,the purpose of connection S0 is to hold the valve in closed positionagainst the action of said spring under high pressure or drivingconditions, and the purpose of connection 51 is to maintain a pressuredifferential for holding the valve in closed position under conditionswhere pressure is reversed in the pump, as in decleration of the pump orof the motor operated thereby, or of both the pump and the motor. Thepurposes and operation of this hydraulic valve will be consideredfurther in describing the operation of the transmission as a whole.

The high pressure pump outlet 42 adjoins a longitudinally extendingopening 52 (Fig. 7) extending through housing member 25 to conduct highpressure fluid from the pump discharge to gear chamber 32. From thischamber the fluid passes into an annular groove 53 in member 25, thencethrough a transverse bore 54 (as indicated by the heavy dotted arrow inFig. 2) into the longitudinal fluid passage 19 of shaft 17. From thispassage it flows through transverse bore 55 into' the motor 16. Lowpressure fluid returning from the motor via passage 20 in the shaft isdischarged at the end of the shaft into chamber 56 formed by a recess incover plate 24 of the pump housing. From this chamber the fluid passesthrough a longitudinal opening 57 through housing member 27 andintersecting low pressure inlet 43 of the pump.

The hydraulic motor 16 (Figs. 2 and 5) is of a con struction similar tothat of the pump 15 but has several pairs of annular cylinders 58, 59and 60 Coaxially arranged. While I have chosen for illustrative purposesa motor unit comprising three pairs of coaxially arranged annularcylinders, it will be understood that the motor may have a lesser orgreater number of cylinders as may bers 25, 26, and 27, and pistonrotors 36. Annular cylinders 38 are connected by a fluid passage 39extending through housing member 26 and around abutment rotor 18. Theabutment rotor has a recess 40 to clear the pistons 37 as they pass theabutment.

be desired, depending upon the type of operation required in aparticular installation. Three pairs of cylinders give fourprimaryspeeds or torque ratios, modified during the transition from onespeed ratio to another by the differential planetary action of theinterconnected motor and pump units, as will appear.

The rotary hydraulic motor, when of the abutment type illustrated,preferably is built up of annular plate-like housing members 61, 62, 63,64, 65, 66 and 67 with end plates 68 and 69 bolted together by means ofa series of tie-rods 70 extending through aligned apertures in thehousing members and also through the end of a flywheel housing 71. Thecomplete transmission may be mounted for example in the main chassisframe of an automobile by means of a flange 72 on the flywheel housing,with the usual couplings to the motor and drive shaft. Piston rotorshafts 73, 74 are mounted in suitable bearings in the motor housing.Fixed to theseshafts are pinio-ns 75, 76 meshing with a gear or gearteeth 77 on shaft 17. Also fixed tov piston rotor shafts 73 and 74 are aseries of piston rotors with pistons-78 slidably arranged for rotationwith the shafts 73 and 74 in the respective pairs of annular cylinders58, 59 and 60. In line with each pair of annular cylinders the shaft 1 7is provided with a recess79 to clear the pistons as they pass the shaft,thus providing a rotary abutment valve for each pair ofcylinders, theserecesses being spaced 120 apart around the shaft 17 in the particularembodiment shown. Each pair of annular cylinders 58, 9 and 60 areconnectedby a. fluid passage 8t? extending through the respectivehousing members and around abutment rotor 17 (see Fig. 5

High pressure fluid discharged from shaft 17 through port 55 enters achamber 81 formed by complementary recesses in end plate 69 and housingmember 67, as indicated by the heavy dotted arrow in Fig. 2. rom chamber81 the fluid enters a passage 82 at the top of housing member 67 andconnecting passages 83, 83 the lower side of body 84 of the automaticvariable control valve indicated. generally at $5 (see Figs. 13 and 14).Fluid entering valve 85; under certain conditions of operation to be'described, next enters one or more of the cylinders of the motor and. isreturned to valve 85. This low pressure fluid then isdischarged throughone of' the pair of passages 87 in body 84 of the valve and enters aconnecting passage ;88 in end plate 68 of -'the motor housing, fromwhich it is discharged into chamber 39 of seal cover plate 9.0: boltedto endplate 68 (see Figs. 12 and 14-). From chamber 89 the lowpressurefluid passes through. a transverseport 91' which is incommunication w-ith a central bore 92 (in the manner indicated by thelight dotted arrow) in shaft 17' connected to. passage 21) at '93. forreturn to the low pressure side of the pump in the manner whichalreadyhas been described;

The. bearings and shaft seals at the adjacent. ends of pump and motor 16are of more or less conventional construction, adequately illustrated inFig. 2 and not requiring detailed description. Shaft 17 rotates in. thefixed motor bearings and also in the movingpump bearings, and pump 15,as we have seen, is bodily rotatable about hc shaf-t.

Refer ing more particularly to Figs. 4, 9, and 10, I shall now describethe preferred construction of: the automatic control valve mechanism andits manual selector. Body casting 84 of this valve is secured to the topof the. motor housing as by means of screws 94. A pair of longitudinallyextending valve channelways 9,5, 96 are formed in body .84 slidably toreceive pistons 97, 98 fixed. to. valve stems 9 9., 161 having enlargedends 1.01, 1&2, slida'bly received in the reducedportions of valvechannelways 95, 9,6; (right-hand end of Fig. 4). for; the high pressurefiuid from the pump are in communication with the reduced portions ofvalve channel.- ways 95, 96. At the left-hand end as viewed in, Fig. 4,the valve channelways are enlarged are in communication with thedischarge passageways 87 for the low pressure fluid returned from themotor. The central portions of valve channe-lways 95, 96 are relieved bya series of annular chambers 1E3,one for each pair of motor cyl-. indersfor each valve channelwa-y. One of a series of inletoutlet ports 104connects each chamber 103 with the inletoutletpassages- 105 of themotor. (These passages are either inlets or outlets depending uponwhether the motor is being driven in the forward, direction or inreverse.) Valve pistons 97- and 98 are urged to the right as viewed inFig. 4 by'means of compression springs 1%, hearing at oneendagainst aseat 187, the position of which'is adjustable by means of a screw 183mthe cover plate 113 at the. end of the. valve body to give the desiredinitial'compres sion, and bearing at its other end against a seat ltithscrewed into thejhollowend of the valve piston. A small passage 110extends through the skirt and; head of the Entering passages 83, 83.

piston, where it joins a central bore 111 in valve stem 99 (or Thisprovides a relief for movement ofthevalve, permitting fluid to flowthrough the piston and valve stem as it reciprocates, preventing huntingactionand avoiding creation of either a pressure lockor a vacuum betweenthe enlarged end 101 (or 192) of the valve stem and the end of thereduced portion of thevalve channelway where it is closed by cover plate112. The skirt of the piston 97 (or 98) of the valve is provided with aseries of peripheral openings 114. An auxiliary. check valve is slidablyreceived within the skirt of the piston to pass from one side to theother of openings 114-. Normally this check valve is held in theposition shown in piston 97 (as viewed in Fig. 4) by means ofcompression spring 116. The purpose of this arrangement is to permitautomatic operation of the valves without locking the fluid flow as thepiston moves to cover or uncover the successive parts 194, and withoutloss of pressure. Whom ever the piston moves into a position which wouldcom! pletely block one of the ports, fluid from the low pressure side ofthe piston enters the interior of the piston, forcing check valve 1.15to the right as viewed in'Fig. 4 and pen. mitting free passage of thelow pressure fluid through. the peripheral openings 97 in the skirt ofthe piston. Another important function of this piston valve constructionis that it maintains pressure on the high pressure side of the. pistonregardless of its position. This is accomplished by the properlongitudinal spacing of peripheralopenings 1-14 in relation to checkvalve 115 such that when the check valve is closed by spring 116, thevalve 115 is to the leftv cf the openings 11%, thus blocking flow offluid through. the piston from the high pressure side of the piston whenthe piston is in a position which would permit high pressure fluid tohow into one of the annular: chambers 10:3 and through openings 114.

The manual selector for forward, neutral and reverse, operationcomprises an arm 117 connected to a cam; member 118 pivotally mounted asby means of a screw 119 to the top of valve body 84 near the ends of thereduced portions of the valve channelways. Inclined cam surfaces 120, inthe under side of member 118 are arranged to engage locking pins 121,122 extending through the top of the valve body at points where therespective pins can be brought into engagement with the. in side of theenlarged portions 101, 102 of the valve stems- 99, 109. In Figs. 4 and9, the manual selector is in forward position in which it holds pin 121downwardly-v against the action of a compression spring 123-. This looksreverse control valve 97 in the position shown in Fig. 9. In this sameposition of the manual selector, pin,- 122 is held in the raisedposition by its spring 123 inwhich;

it is out of engagement with the enlarged end 102 of the forward controlvalve 93, permitting thisvalve tooperate in response to changes in thefluid pressure discharge: from the pump. When the manual selector is.movedzijnto v the neutral position indicated by thelegend on Fig. 4, i.e. by bringing the axis of selector arm 117 into the position shown bythe dash line marked Neutral, pin 1'21--is partially raised and pin 12;.partially lowered through the action of cam surfaces 120, freeing bothvalves. When the manual selector is moved into the reverse positionindicated by the legend in Fig. 4, pin 122 is com;-

pletely depressed to lock forward control valve 98 in: its

fully closed position while pin 121 is fully raised to free. theautomatic action of the reverse control valve 97..

Operation Referring to Fig. 14, 1 will now describe the mode ofoperation of the complete hydraulic transmission as applied for exampleto highway vehicles.

shaft 17, 18 has been shown separately, and the view of course is notdrawn to scale.

The part of the view at the right-hand which is bracketed at at the topof the sheet, represents the pump unit 15, and the part which isbracketed at 16 represents the motor unit 16. The automatic variablehydraulic control valve 85 has been separated into two parts at the topand bottom of the view. In operation only one of the control valves 97,98 is freed for automatic operation at a particular time (except inneutral when both are free), depending upon whether the car is to bedriven in forward or in reverse, but in either case the oil flowsthrough both of the sections of the valve, as will appear.

Let us assume that the car is parked on a level stretch of roadway andthat the operator Wishes to start the car in the forward direction. Hewill first see that the control arm 117 (Fig. 4) is placed in neutralposition. He will operate this control from a suitable lever or plungerarranged on the steering post or dashboard of the car, and if desiredthis control can be electrically interlocked with the electric startermechanism for the internal combusion engine, making it impossible tostart the engine unless the control is in neutral position. He thensteps on the starter which engages teeth 86 (Fig. 2) of the pumpflywheel unit, spinning shaft 22 to start the engine. With the enginerunning at idling speed, the operator now moves the control or selectorto bring arm 117 into the forward position shown in Fig. 4. This bringslocking pin 121 into the position indicated in all of the drawings andwhich can be seen in the diagram, Fig. 14, with pin 122 retracted. Thuscontrol piston 97 is locked to the right, while piston 98 is free tomove. At idling speed the automatic pump bypass valve 46 will be in theopen position shown in Fig. 6 where it is held by the action ofcompression spring 49. With this valve open, fluid discharged from thehigh pressure outlet 42 of the pump is free to flow through by-pass 41into the low pressure inlet 43 of the pump and does not create drivingpressure on the motor. Consequently as the pump unit is bodily rotatedabout the axis of the stationary drive shaft 17, 18 in the directionindicated by the arrow :1, the resulting pumping action merely drivesthe fluid through the pump circuit via the by-pass 41 without exerting adriving action on the motor 16. Hence control piston 98 of the motorunit remains in its extreme right-hand position under the action of itscompression spring 106.

The operator new steps on the accelerator, increasing the R. P. M. ofthe pump. This builds up the pressure at the high pressure outlet 42 ofthe pump to the point where the increased pressure transmitted via bore50 to the end of differential piston valve 46 is suflicicnt to move thevalve to the right as viewed in Fig. 14, and into the position thereshown against the action of spring 49 to close lay-pass 41. When thisoccurs, high pressure fluid discharged from pump outlet 42 is forcedinto passage 52 leading to gear chamber 32 surrounding shaft 17, 18 fromwhich it enters shaft passage 19 to be discharged into gear chamber 81of the motor. From this chamber the fluid passes through port 82 whichis in communication with connecting passages 83 of control valve 85.However, since control piston 97 is locked in the position shown in thediagram, the driving fluid must seek an outlet through that one of theconnecting passages 83 which leads into the cylinder of control piston98. The effective cross-sectional area of piston 98 is greater than theeffective cross-sectional area of the enlarged head 102 of the valve,and the pressure differential thus created moves piston 98 to the leftas viewed in Fig. 14 against the action of compression spring 106. Howfar it will move depends in part upon the force required to start thecar in motion and in part upon the rate of acceleration of the primemover. Under conditions of high acceleration, piston 98 will be moved tothe left far enough to uncover allof the connecting ports 104. Thus theforce of the high pressure fluid from the pump will be distributedbetween the cylinders 58, 59 and 60 of all three sections of the motor,producing the maximum starting torque ratio. The fluid entering themotor through ports 104 drives the pistons, producing rotation of gearedabutment and drive shaft 17 in the direction shown by the arrows. In theevent the operator should accelerate too rapidly, or under anyconditions of operation which would tend to stall the prime mover oroverload the transmission or drive shaft of the car, sufiicient pressureis built up in the hydraulic circuit to move piston 98 into a positionwhich uncovers relief passages 124 leading to passage 87. This permitssome of the driving fluid to by-pass the motor for direct return to thepump, until the pressure is reduced within safe operating limits whenthe piston 98 returns to one of its normal operating positions, closingthe by-pass.

As soon as the drive shaft begins to turn, starting the car forward,rotary element 18 of the pump also turns with the shaft in the directionshown by the arrow. It will be observed that the direction of rotationof element 18 is the same as the direction of bodily rotation of thepump (arrow a). Consequently for a given speed of drive shaft 22, rateof fluid discharge from the pump remains constant only so long as driveshaft 17, 18 is at rest or is rotating at a constant speed, because asshaft 18 begins to rotate or as its speed is increased, the differentialbetween the speed of bodily rotation of the pump and rotary element 18thereof is decreased. This is a planetary system in which rotary element18 of the pump is the sun gear and the piston rotors are the planets.The torque ratio between shaft 22 and shaft 17, 18 is infinitelyvariable in accordance with the rate of acceleration of the car ineither a forward or reverse direction.

Now, as the differential between the rate of rotation of the pump aboutits axis and the rate of rotation of the rotary element 18 of the pumpabout the same axis decreases, the rate of discharge of high pressurefluid from the pump decreases, decreasing the pressure in the system.When the pressure has been decreased by a predetermined amount throughthis action, or through decreasing the speed of drive shaft 22, controlpiston 98 will be moved to the right as viewed in Fig. 14 to close oneor more of the ports 104 and thus to cut out one or more sections of themotor unit. In its extreme left-hand position we have seen that allthree sections of the motor are being driven. As

the piston 98 begins to move to the right, cylinders 58 are first cutout of operation. Further movement will also close the port to cylinders59, leaving only cylinders 60 in operation. This is the conditionillustrated in Fig. 14. When one of the sections of the motor has beencut out of the high pressure circuit in this manner, that section beginsto act as an idling pump due to the continued rotation of shaft 17, andthe fluid from the discharge of the pump simply passes around throughvalve and passages 87 and back into the cylinders without appreciableresistance to the flow.

With motor sections 58, 59 and 60 all operating in the high pressurecircuit-i. c. with valve 98 to the extreme leftthe transmission is inwhat might be described as low gear. With sections 59 and 60 only actingin the high pressure system, we could then refer to being in secondgear. Similarly with section 60 alone operating in the high pressuresystem, we have third gear, and after all of the sections of the motorhave been cut out of operation we are in fourth gear.

While I have shown and described a transmission embodying a motor withthree driving sections arranged in parallel, it will be understood thata greater or fewer number can be employed as may be desired, dependingupon the conditions of operation for which the transmission is designed.In some cases it may be desirable to have as many as seven or eightsections.

I will now describe in greater detail the operation of what we havecalled fourth gear, that is, with all of the ports -lM closed sd thatall of the 'cylinder sections are operating as circulating pumpsundersubstantially no-load driving speed alon'ga' levelstretchof road,the pressure in "theisystem being sufiiciently low for piston 98to'beheld in its "extremerighvhand position by'the spring 106.

'When'the piston is in this position there can of course be no fluidflow from thepump through the motor'unit.

The pump'is therefore compelled to rotate bodily on its axis at the sameor substantially the same speed as' shaft17,'18,"under"which'con'diti'onno pumping action will occurjan'd' ineffect we have a direct drive from the engine 'shaft'22 throughthelocked'hydraulic system to driven 'shaft*17of' themotorgproducingmaximum e fliciency. It'niay'be observed at this point that throughoutthe operation of my transmission the hydraulic driving action isextremely-positive. That is,'there cannot be any'substantial amount ofslippage because the driving fluid is always locked between themechanical elements. Moreover the final locking action which occurs inthe top driving speed, i. e. at the lowest torque ratio, takes placeentirely automatically and without the use of any sort of auxiliarymechanical clutch.

If it is desired to pick up speed rapidly as, for example, in passinganother car, the driver will of course depress the accelerator sharply.This will increase the pressure in the system sufficiently to movepiston 98 to the left and bring one or more of the sections of the motorinto operation to increase the torque ratio and permit rapid pickup inthe driving speed.

Now let us assume that the car reaches a downgrade and that theoperator, wishing to hold down the speed, removes his foot from theaccelerator. Piston 98 remains in its extreme right-hand position. Allof the sections of the motor are, as we have seen, acting as idlingpumps under no-load condition. Consequently the motor, so to speak, isfree wheeling. However since rotary element 18 of the drive shaft istrying to rotate faster than the speed of bodily rotation of pump 15,pressureis reversed within the pump, creating pressure at what isnormally the inlet 43. This pressure will be transmitted via bore 51 tothe center of pump by-pass valve 46 and, due to the differentialpressure created by reason of the different effective areas of thepistons 47 and 48,

- will maintain the clutch valve in its closed position.

The result of this is to generate in the pump that amount of pressurewhich is required to turn the engine at a speed generated by themomentum of the car. Thus free Wheeling is prevented through the actionof the diflerential valve of the automatic clutch, and the brakingaction of engine compression can be utilized.

To drive the car in the reverse direction, the operator will move theselector to bring arm 117 into the reverse position shown in Fig. 4,releasing pin 121 and depressing pin 122 so that piston 97 is free tomove in response to pressure while piston 98 will be locked in itsextreme righthand position. Changes in the torque ratio within the motorunit for operation in reverse occur in the same manner as has beendescribed with reference to forward operation.

From the foregoing description it will be understood that the operationof the automatic variable control valve of the motor unit changes thetorque ratio as one or more of the motor sections are brought intooperation or taken out of operation. The differential planetary actionof the bodily rotating pump unit and rotary element 18 of the driveshaft 17, as we have seen, produces an infinitely variable torque ratiowhich is superimposed upon, or modifies, the variation in torque ratiobrought about by operation of the automatic control valve.

It will be understood that the hydraulic system I have described isfilled with any suitable driving fluid such as pump outlet' -to the pumpinlet under low pressure-idling conditions and "for "closing the bypassto transfer iluid to theniotor' under' high pressure drivin'g'conditions, said hydraulically actuated valve "comprising "two connectedpistons "of -'differe'rit fiective "areas to create a pressuredifferential}the by pass being arranged to be closedby one of the twopistons, and a fluid connection on the low-pressure side of the valvearranged to create a pressure difierential and close the bypass underconditions where pressure is reversed in the pump as in deceleration ofthe machine operated by the transmission.

2. In a transmission of the class described, a rotary hydraulic pumphaving a high pressure fluid outlet and a low pressure fluid inlet, aby-pass connecting said outlet with said inlet, a differential pressurepiston valve in said by-pass, spring means normally holding said valvein open position under low pressure idling conditions, a fluidconnection from said outlet to one end of said differential pressurepiston valve for holding said valve in closed position against theaction of said spring means under high pressure or driving conditions,and a second fluid connection from said inlet to another portion of saiddiiferential pressure piston valve to maintain a pressure differentialfor holding said valve in closed position under conditions wherepressure is reversed in the pump as in deceleration of the pump.

3. An automatic variable torque hydraulic transmission comprising arotary hydraulic pump section and a rotary hydraulic motor sectionhydraulically coupled through pressure and return lines in a closedpositive hydraulic system in which the pressure line from said pumpsection leads to both sides of said motor section and the return line tosaid pump section leads from both sides of said motor section, valvemeans comprising two pressure actuated valve units, the pressure lineand return line at each side of said motor section being controlled by arespective one of said valve units, said rotary hydraulic motor sectioncomprising rotary fluid power members connected in parallel to one ofsaid valve units at one side of said motor section and to the other ofsaid valve units at the other side of said motor section, said two valveunits also being connected to one another by a fluid conduit, and amanual selector movable to alternate settings in which each of the valveunits can be selectively held in a position which opens the return linebetween said rotary fluid power members and the inlet of said rotaryhydraulic pump section for free exhaust at one side of the motor sectionwith the pressure line closed off while the other of said valve units isoperable in response to changes in hydraulic pressure in the pressureline to admit fluid to one or more of said rotaryv fluid power members.

4. An automatic variable torque hydraulic transmission comprising arotary hydraulic pump section and a rotary hydraulic motor sectionhydraulically coupled through pressure and return lines in a closedpositive hydraulic system in which the pressure line from said pumpsection leads to both sides of said motor section and the return line tosaid pump section leads from both sides at-each side of said motorsection being controlled by a respective one of said valve units, saidrotary hydraulic motor section comprising rotary fluid power membersconnected in parallel to one of said valve units at one side of saidmotor section and to the other of said valve units at the other side ofsaid motor section, said two valve units also being connected to oneanother by a fluid conduit, a manual selector movable to alternatesettings in which each of the valve units can be selectively held in aposition which opens the return line between said rotary fluid powermembers and the inlet of said rotary hydraulic pump section for freeexhaust at one side of the motor section with the pressure line closedoff while the other of said valve units is operable in response tochanges in hydraulic pressure in the pressure line to admit fluid to oneor more of said rotary fluid power members, and the pump section havinga by-pass conduit between its inlet and outlet and an automatichydraulically actuated valve in said by-pass conduit operable inresponse to changes in fluid pressure within the pump section.

References Cited in the file of this patent 1 UNITED STATES PATENTS SneeAug. 22, Keene Feb. 22, Bair Oct. 5, Chamberlain et a1 Apr. 23, DeMillar Oct. 13, Thoma Apr. 30, Sigmund et a1 Aug. 17, Corrigan Sept. 14,Roth Dec. 21, Doran Feb. 27, Doran Apr. 24, Fullerton Apr. 2, Wemp Aug.10, Berry Jan. 2, Moran Nov. 6,

